This invention relates generally to a dental device, and more particularly to an intra-oral dental device.
Still more specifically, the invention relates to an intra-oral aligning assembly for tooth prostheses, occlusion diagnostic and/or occlusion therapy in general, and more particularly to such an assembly which includes rigid upper jaw and lower jaw components of which one is provided with a through-going tapped bore into which a supporting pin is threaded, the tip of which is insertable into an opening in the area of that surface of the other jaw plate which faces the jaw plate having the tapped bore.
Aligning assemblies of this type are known, for example from U.S. Pat. Nos. 3,068,570 and 3,564,717. When assemblies of this type are used, the two plates are inserted into and fixed in the upper and lower jaw, respectively. Thereafter, the patient is requested to cause his lower jaw to perform sliding movements in anterior-posterior as well as lateral direction, and during these movements the tip of the supporting pin traces on preferably colored surface of the other jaw plate a figure having essentially an arrow-shaped configuration and which is called a Gothic Arch. Thereafter, the dentist places a thin apertured plate onto the other jaw plate in such a manner that the middle of the opening of the apertured plate coincides with the tip of the arrow. In this position the apertured plate is fixed with respect to the other of the jaw plate and thereafter the other jaw plate is again inserted into the mouth of the patient who is then instructed to close his jaws with slight pressure, the purpose being to have the tip of the supporting pin enter into the opening of the apertured plate. The dentist then places dental molding material or the like between the two bite plates in order to fix them in this position relative to one another. After the material hardens the bite plates can be taken out of the patient's mouth as a unit, i.e. in a state in which they are fixed relative to one another.
In the devices known from the prior art the tip of the supporting pin is formed by a sphere which is turnably journalled in an appropriate journal of the tip of the pin shaft. In this manner the pin is constructed somewhat analogously to a ball-point pen, so as to assure that during tracing of the Gothic Arch rolling of the sphere produces ready movement of the tip of the pin with respect to the other bite plate. Of course, the sphere or ball must be so mounted that during the use of the assembly it does not fall out of its support, which means that it must enter the socket holding it to a depth which is greater than its radius.
The opening and closing movement of the lower jaw takes place over a range of approximately the first two centimeters (adjacent the closed position) in a circular path about a center formed by the condyles. The position of the condyles is defined by the concept of the retrograde contact position, which is the starting point of each functional analysis and prosthetic treatment. Therefore, it must not be allowed to change in the determination of the bite height, because it determines the vertical position of the lower jaw with reference to the upper jaw.
Since the opening and closing movement of the lower jaw with the condyle position in retrograde contact position takes place in a circular path, this circular path must be taken into account during the point-like fixation of the selected bite height. Any lack of accuracy in the vertical direction results in an improper bite height, whereas any lack of accuracy in the horizontal direction produces a false condyle position.
With respect to the known assemblies of the type here in question, the accuracy is limited. During the terminal bite position the tip of the supporting pin will meet the arrowhead traced on the other bite plate in cooperation with the opening of the apertured plate in an exact manner only, if the bite plates and the axial directions of the supporting pin tip and the apertured plate opening approach one another in exact parallelism at the end of the jaw movement. Such an exactly parallel approach of the bite plates, the supporting pin tip and the opening in the apertured plate in the terminal phase of the circular movement of the lower jaw cannot be assured in actual practice. It is obtained only in certain fortunate exceptional conditions. In the vast majority of cases the tip of the supporting pin will engage the edge or the inner wall of the opening in the apertured plate prematurely, due to tilting of the pin with reference to the axis of the opening. This results in a wedging effect and a maladjustment of the supporting pin tip and the arrowhead tip. The result is improper registration during the fixation both in the vertical direction (bite height) and in the horizontal direction (condyle position). This results in a condyle shift which is undesirable.
One of the objects of the invention is to eliminate these problems and to produce a device of the type in question which is simple to use and which excludes registration errors to the maximum extent possible, which result from the fact that in the terminal phase of the bite movement deviations with respect to parallelism of the bite plates occur and the circular movement of the lower jaw during the closing movement has a forwardly directed component.
Another disadvantage of the known devices is that the bite plates can be only insufficiently fixed in the upper and lower jaws, because the bite plates are constructed either as narrow strips, or triangular or of hour-glass shape. This means that they have few supporting areas which are closely adjacent to one another, so that there is a substantial danger that the bite plates may tilt during the tracing of the Gothic arch and during the final bite.
The determination of the joint-related position of the lower jaw with reference to the upper jaw, during which heads of the jaw joint are centered at the highest points of the cavities of the jaw points, is effected according to the static principle of the three-point support and requires that the supporting pin is centrally arranged. If the supporting pin deviates from the central arrangement in the saggital or transversal direction, a tilting of the lower jaw results which causes a shifting of the heads of the jaw joint in their sockets. This clinical experience is used in the treatment of patients who have the symptoms of myoarthropaty and for whom the heads of the jaw joint are to be therapeutically displaced in the sockets until a reduction of pain or freedom of pain during the final bite has been achieved. In the known devices the supporting pin is adjustable with reference to the bite plate carrying it, only in the direction of the supporting pin axis, which is normal to the bite plate plane. If a change in the supporting pin position is desired in the saggital or transversal directions, the bite plate must be removed from the supporting substrate and subsequently be connected again thereto. This is time consuming and inaccurate, because there is no appropriate reference system.
In German published application No. 2,645,852 it has been proposed to provide an aligning assembly with a three-dimensionally displaceable supporting pin. A threaded sleeve receiving the supporting pin is movable in longitudinal direction of an elongated slot of an intermediate plate and can be fixed with reference to the intermediate plate by means of a set screw. The intermediate plate itself is adjustable in a direction normal to the elongation of the elongated slot, by means of a guide which is inserted in the respective bite plate. To fix the intermediate plate two clamping screws and bars are provided at opposite sides of the intermediate plate which serve to press the bars against the intermediate plate and are threaded into the bite plate. This solution, however, is rather expensive and, in addition, requires a very significant amount of space.
When taking a bite using intra-oral aligning assemblies, it is desired that the retrograde contact position of the condyles in the sockets are fixed under the same pressure loads on the gums and the teeth, as they occur if a definitive tooth replacement is provided. Loading of the gums and of the teeth during the taking of the bite is to correspond to the later loading by the prostheses. This requires readily workable types of bite plates which can reach any desired point of the dental arc and be there positioned. The known devices are too small and too narrow for this purpose and as a consequence disadvantageous tilting moments can arise during the registration and fixation.
For this reason another object of the invention is to provide an intra-oral assembly device of the type in question the bite plate of which can be mounted particularly safely in the upper and lower jaws. Furthermore, the device is to have a three-dimensional adjustability of the supporting pin in a simple manner. The device is to permit a prostheses-simultaneous mounting and to require little room.